typical air conditions for planning purposes

[hotrod]

I just wanted to ask those of you who have kept notes on weather conditions out on the salt some questions regarding "typical air conditions".

At the local drag strip, I have kept notes for several years regarding absolute barometer, temperature etc. I found that on the majority of race days, only 2 or 3 absolute barometer readings and a narrow range of temperatures dominate all the others in frequency. After analyzing those numbers, for planning purposes, I defined a "standard day at the track"  with its typical absolute pressure and temperature.

Due to both the impact of air density on power and aerodynamic drag I would like to get a handle on what the combined experience of the board thinks would define a " typical day on the salt."

According to standard atmosphere tables,

Absolute barometer should range from:
25.84 in Hg -- to -- 25.37 in Hg
656 mm Hg -- to -- 644 mm Hg

Absolute pressure
12.69 psi -- to -- 12.46 psi
0.892 kg/cm^2 -- to -- 0.876 kg/cm^2


I'm guessing that 80% or so of the runs are made at temperatures that
range from 65 deg F - 105 deg F

Humidity's I would guess typically are a bit wetter than normal (due to evaporation off the salt)  for high desert environments so would perhaps run from 30% - 60% RH during weather likely to allow runs to be made.


I am curious if those of you who have been attending for years concur with those ranges and if you might venture a guess on what you would consider a "typical mid day run condition during speed weeks".

I am most concerned with the typical conditions during the 10:00 - 2:00 time period when the weather is good ( hot clear and moderate to low wind conditions ) like it was most of this years speed weeks.

Yes I know it varies widely from year to year, yes I know it can be very hot and very cold and wet, but I'm looking for the "typical good race day".

Larry

[edweldon]

Larry--Most of the guys running fuel and/or low-tech hilborn fuel injection systems keep pretty close tabs on temperature and barometric changes.  Some with aviation experience talk in terms of density-altitude which is calculated from pressure, temperature and humidity.  Bottom line here is that humidity doesn't efect things a whole lot; so you seldom see people swinging psychrometers at the Salt.  What you do see is adjustments (pill changes for the Hilborn guys) to mixture between the cool mornings and the hot early afternoons; less so into the late afternoon.  I don't need to keep such records.  But hopefully a racer that does will tune in here and give you some real numbers to chew on.
Ed Weldon

[Glen]

We don't keep a daily chart on the DA at speed week. Each run is posted with the DA  on the time slip. There is also a weather station at the fuel truck and many racers have their own weather stations.

[Sumner]

Here are some numbers for you from our runs:

Day....Time......Humidity..Density Altitude...Temp.

8-12...1:07pm.....21%.........6820 ft.............81 deg      
8-12...5:54pm.....13%.........7407 ft.............90 deg
8-13...5:43pm.....13%.........8160 ft.............83 deg
8-14...3:02pm.....16%.........7977 ft.............89 deg
8-15...11:59am...17%.........6867 ft.............84 deg
8-16...10:32am...13%.........6350 ft.............76 deg
8-17...7:17 am....26%.........5707 ft.............64 deg
8-17...2:24 pm....13%.........6711 ft.............84 deg
8-17...4:57 pm....11%.........6794 ft.............85 deg

One thing I noticed is that when we got fuel once the DA at the fuel trailer was about 5900 ft..  We ran a couple hours later and the DA on the time slip was the 8160.  I wondered if it could change that much in 2-3 hours or if there is something else wrong.

Above the last two runs were lic. runs with Patrick on the short course.  On the 16th we qualified and were pretty rich.  The next morning we leaned it out on the pill from I think a 105 to a 110 but according to our air/fuel data we were even richer even though the DA went from 6350 on the 16th to 5707 on the 18th, which I would have thought would have made it leaner yet.  Looking at the Humidity though it went from 13% on the 16th to 26% on the 17th.  

If there is more moisture in the air is there then less oxygen to burn making it richer???

c ya, Sum

[PorkPie]

Sum,

when we run some years ago the streamliner, we changed the jet's sometimes three times during the time when we was in the waiting starting line, due to the change of density, pressure, temperature....

I told this also to Ron Ayers, that this is a special situation (irritation) at the salt....

[hotrod]

One thing I noticed is that when we got fuel once the DA at the fuel trailer was about 5900 ft.. We ran a couple hours later and the DA on the time slip was the 8160. I wondered if it could change that much in 2-3 hours or if there is something else wrong.

Good info that is exactly what I'm looking for --- a few more of those would give folks a good basis for planning.

Regarding your comment above. I've seen the same thing at the drag strip here in Colorado.
In Sept 03 I was drag racing up here at Bandimere's and the first two runs were at an absolute barometer of 23.41 the next run was at an absolute barometer of 22.35 in Hg --- this change occurred in the time it took to pick up my timing slip at the end of the second run, drive to staging and make the third run -- perhaps 10 minutes. We had a frontal passage (brief gusty wind) but no significant temp change 59 Deg F to mid 60's.

I am a bit surprised to see the humidity's are down to normal summer time humidity's you see here in the high desert areas of the country.  I expected to see them a bit higher due to the water evaporating off the salt would have pushed them up about 10% or so.

Thanks for the data, I would appreciate a couple more lists like that from folks at  other speed weeks as well to see if it changes much year to year.

Larry

[Sumner]

Here is also the SP in inches for those runs (same order):

25.55
25.47
24.57
24.99
25.62
25.61
25.67
25.70
25.67

c ya, Sum

[hotrod]

Just thought I'd post up this image of the ERC data board at the fuel trailer for those that have not seen what info is available.



Larry